Recently, a secondary battery, which can be charged and discharged, has been widely used as an energy source for wireless mobile devices. Also, the secondary battery has attracted considerable attention as a power source for electric vehicles and hybrid electric vehicles, which have been developed to solve problems, such as air pollution, caused by existing gasoline and diesel vehicles using fossil fuel.
Small-sized mobile devices use one or more unit cells, for example, three or four unit cells, for each device. To the contrary, medium- or large-sized devices, such as vehicles, use a battery pack comprising a plurality of unit cells electrically connected with each other as a high-output, large-capacity battery is required.
Generally, a plurality of unit cells, which are connected in series or parallel with each other, are mounted in a cartridge, and a plurality of such cartridges are electrically connected with each other. In this way, a battery pack is manufactured.
FIG. 1 is a perspective view illustrating an exemplary structure of a cartridge having four unit cells mounted therein.
Referring to FIG. 1, the cartridge 100 comprises a pair of frames 120 and 122, which are attached to each other. The unit cells 200 and 201 are located in cell partitions 130 of the frames 120 and 122 while the frames 120 and 122 are separated from each other, and are then securely fixed at the cell partitions 130 of the frames 120 and 122 after the frames 120 and 122 are attached to each other. The unit cell 200 has an electrode lead (not shown), which is electrically connected to that of a neighboring unit cell 201 via a bus 140 located at the upper part of the cartridge 100. As shown in FIG. 1, the unit cells 200 and 201 are connected in series with each other, although the unit cells may be connected in parallel with each other. The unit cells are electrically connected to a cathode terminal 150 and an anode terminal 160, which protrude at opposite sides of the upper end of the cartridge 10, respectively.
FIG. 2 is a typical view illustrating the electrical connection of cartridges in a conventional battery pack.
Referring to FIG. 2, a plurality of unit cells (not shown) are mounted in each of the cartridges 101, 102, 103 . . . 110 in the same fashion as shown in FIG. 1. The cartridge 101 is provided at opposite sides of the upper end thereof with a cathode terminal 151 and an anode terminal 161. To accomplish the electrical connection between the cartridges 101, 102, 103 . . . 110, the first cartridge 101 is stacked on the second cartridge 102 while the first cartridge 101 and the second cartridge 102 face each other such that the cathode terminal 151 of the first cartridge 101 is adjacent to an anode terminal 162 of the second cartridge 102. The electrical connection between the cartridges 101, 102, 103 . . . 110 is performed by bus bars 170. The bus bars 170 are fixed to the respective terminals of the cartridges by welding. Also, the second cartridge 102 is stacked on the third cartridge 103 while the second cartridge 102 and the third cartridge 103 face each other such that a cathode terminal 152 of the second cartridge 102 is adjacent to an anode terminal 163 of the third cartridge 103. In the same manner, the other cartridges 104 . . . 110 are stacked one on another in order while the cartridges 104 . . . 110 face each other. The anode terminal 161 of the first cartridge 101 and a cathode terminal 150 of the last cartridge 110 are connected to a battery management system (BMS), which is not shown in the drawings. The cartridges 101, 102, 103 . . . 110 are stacked one on another while the cartridges 101, 102, 103 . . . 110 face each other as described above, and therefore, a high-output battery pack 300 having a plurality of unit cells connected in series with each other is completed.
However, the battery pack 300 with the above-described structure has the following problems because the connection length between the terminals 151 and 162 of the two neighboring cartridges (for example, the cartridges 101 and 102) is very small, and the distance between a terminal connection part (first connection part) 401 for connecting the terminals of the neighboring cartridges 101 and 102 and another terminal connection part (second connection part) 402 for connecting the terminals of the neighboring cartridges 103 and 104 is also very small.
First, it is difficult to connect the terminals. The thickness of each cartridge is nearly equal to that of the unit cell. As a result, the connection length between the terminals of the neighboring cartridges is very small when the cartridges are stacked one on another. Consequently, a process of connecting the terminals, which are very close to each other, and a process of forming the terminal connection parts without affecting the neighboring terminal connection parts are time-consuming and require high precision, thereby significantly reducing the manufacturing efficiency of the battery pack.
Secondly, when the terminals are connected with each other using electric wires, the structure of the battery pack is very complicated. Furthermore, the electric wires may be connected to each other, and therefore, interference between the electric wires occurs.
Thirdly, the terminal connection parts are concentrated at one side of the battery pack. As a result, the second terminal connection part must be formed in the vicinity of the first terminal connection part. Consequently, a possibility of electric shock is very high.
As described above, the conventional battery pack has several structural problems, and therefore, a battery pack having a new structure solving the problems is required.